not as such no. (and sorry to be picky they are not sponsors)
the owner has to pay for the site and its bandwidth from his own pocket.
how ever with google ads, you register with google and you then put the code on your website. (you have various options, colour number, lay out etc)
when some one clicks on an ad (they dont have to buy anything) the owner of that ad gets charged.
The person displaying that ad then gets a small % of that charge
when it reaches £100 (for UK people) google send you a cheque, or carry it over to the next month if it doesnt make £100
this money is then youirs to do with as you please, but its a fair bet to say the owner pays for the website with it
The ads are chosen automaticaly by google, it reads the page hidden text and chooses something apropriate to the text it finds
I am not sure how the deal with
screwfix works, but i suspect its not that hard.